But no airline has yet introduced biofuels into regular passenger flights. Standards body ASTM cleared the way for that to happen last Friday when it issued final approval for jet biofuels.

Barring another airline beating them to the punch, Lufthansa will become the first to use them regularly.

It will use a 50/50 blend of biofuel and conventional fuel on 8 of its daily 28, 50-minute flights between Hamburg and Frankfurt over the next 6 months.

Lufthansa has dedicated one 200-passenger two-engine Airbus A321 to the 244-mile route. One engine will run on the blend, supplied by Finland’s Neste Oil, and the other on conventional kerosene fuel. The airline has not modified either engine.

Why just one engine, and not both? Does that represent a lack of confidence?

Dünhaupt said that the dual fuel use on the same aircraft gives the airline an opportunity to compare the performance of the separately fed engines under exactly the same flying conditions over the 6 months.

The ASTM certification and Lufthansa flights come about 3 months later than originally expected, as ASTM delayed its approval while the industry conducted further tests.

The 50% blend is the highest ratio permitted under ASTM specifications. Biofuels do not contain the critical sulphurs and aromatics present in hydrocarbon fuels that prevent leaks in engines, tanks and pipes. Aromatics tighten engine seals by swelling them, for instance.

A 50% blend assures enough sulphurs and aromatics, according to Dünhaupt.

Biofuels also have a lower density than ASTM’s minimum requirement.

Lufthansa has been eagerly awaiting ASTM approval. It has already purchased 800 tons of Neste’s NExBTL blend, which is sitting in a tank at the Hamburg-Fuhlsbüttel Airport.

That’s enough fuel to cover the 1200 or so flights over the 6 months, Dünhaupt said. He would not reveal how much Lufthansa paid for the fuel, except to say it was “more than double” the price of conventional kerosene-based fuel.

Lufthansa is spending €6.6 million on the flights, a “large percentage” of which is fuel, Dünhaupt said. Other costs include monitoring equipment to help measure engine performance.

Jet biofuel prices can be vastly more expensive than conventional jet fuel, but should decline as suppliers like Neste, Honeywell UOP and others ramp up production.

Neither Lufthansa nor Neste would yet reveal the “feedstock” for the biofuel. Dünhaupt would only say that the fuel does not come from palm oil.

“We have to leave some news for the day,” Dünhaupt said.

Neste, an €11.9 billion ($17 billion) oil company, uses a variety of sources including rapeseed oil – a common variety is known as canola in N. America - palm oil and animal waste, among others.

The industry is experimenting with various sources to minimize competition for food and water. These include inedible plants like camelina and jatropha, as well as microalgae.

“Our interest is to have sustainable resources in the future, to have an alternative to offer flights at affordable prices to everyone,” Dünhaupt said. Lufthansa estimates that the 1200 flights will save 1500 tons of CO2.